This application claims the benefit of German Application DE P 100 32 440.1 filed Jul. 4, 2001.
The present invention relates generally to a rotor spinning device with a contactless, passive, radial bearing for the spinning rotor and with a damping device embodied for damping radially directed oscillations of the spinning rotor. More particularly, the present invention relates to such a rotor spinning device wherein the damping device comprises a sensor arrangement, a control arrangement and an operating arrangement, with the operating arrangement being designed to act on the rotor shaft at least at one active site.
So-called passive magnetic radial bearings, wherein the seating of the bearing is accomplished by means of permanent magnets, require a considerably reduced capital outlay in comparison to actively controlled magnetic bearings. With passive magnetic radial bearings, a static stability exists in the radial direction. However, the radial dynamic stability is small. Each excitation of the bearing system leads to undesired weakly damped oscillations. An improvement of this state can be achieved by additional oscillation damping.
A passive oscillation damping of radial oscillations is known from German Patent Publication DE 195 43 745. In this case, the stator magnet of a magnetic bearing is resiliently suspended by telescopic legs. A mechanical friction arrangement is provided for damping those oscillation movements of the stator magnet, which oscillate in a plane parallel with the magnetic faces of the rotor and stator magnets. Friction commences starting at a defined value of the oscillation amplitude. No damping takes place as long as this value has not been reached. Damping beginning with such a delay is an obstacle to a permanent low-oscillation running of the rotor.
German Patent Publication DE 29 19 236 C2 describes a magnetic floating bearing for a rotor, wherein a passive radial stabilization takes place by means of permanent magnets. Damping is achieved by eddy current losses in the manner of an eddy current brake.
German Patent Publication DE 198 19 767 A1 defines the basic type of rotor spinning device to which the present invention pertains and describes a damping device for passive radial bearings of spinning rotors. Damping is performed by means of a friction mechanism, whose friction components have frictional surfaces which can be acted upon mechanically. One of the friction components is radially fixed in place on a bearing element, and the other friction component is held in a manner for radially length-adjustability. The radially length-adjustable friction component has a bearing component which encloses the rotor shaft of the rotor. The appearance of large oscillation amplitudes, wherein the rotor could come in contact with the stator, is prevented by this bearing component. The damping converts the occurring oscillations into friction.
With the known oscillation damping systems described, only a too small or otherwise imperfect damping effect can be achieved. In German Patent Publication DE 198 19 767 A1 an active damping is mentioned as a further possibility for damping contactless seated bearings. However, the document does not provide any further suggestions as to how such an active damping is to be designed. It is only pointed out that a relatively large effort is necessary for active damping.
Wear occurs in connection with damping devices operating by means of frictional effects, which requires additional maintenance, or the replacement of wear elements. If the damping generated frictionally has been set too strongly, the danger arises that no damping is provided by the damping device and instead, with passive bearings, damping occurs in an undesired and completely unsatisfactory manner by the magnetic bearing itself. If damping has been set too weakly, the damping effect is poor even when the damping device operates. For this reason, an optimum is determined when setting the damping effect. So-called damping images, from strong to weak, are set depending on the requirements. The cooperation of the elements of a friction mechanism, by means of which a defined damping value, or a defined damping factor, is set, is a function of the material, temperature, aging and friction, and therefore cannot, or only imperfectly, be reproduced. It is necessary for this reason to repeatedly perform an elaborate optimization.
It is accordingly an object of the present invention to improve the damping of radial oscillations of a spinning rotor seated by means of passive magnetic bearings without extravagant expense.
In accordance with the invention, this object is attained by means of a rotor spinning device comprising a contactless, passive, radial bearing for the spinning rotor and a damping device for damping radially directed oscillations of the spinning rotor. The damping device comprises a sensor arrangement, a control arrangement and an operating arrangement, with the operating arrangement having at least two stationary magnetic operating elements arranged to act at least at one active site directly on a magnetic element fixedly connected with the rotor shaft for rotation therewith. The rotating magnetic element comprises an operative element of the passive bearing of the spinning rotor.
An extraordinarily efficient and rapidly effective damping of radially directed oscillations of the spinning rotor is possible by means of the device in accordance with the invention. Improved quiet running of the spinning rotor can be achieved in this way.
A particularly low structural expense outlay is sufficient for a device in accordance with the invention, because the rotating magnetic element on which the operating elements act is an operative element of the passive bearing of the spinning rotor. To improve the damping effect, the active site is located near the end of the rotor shaft.
In a preferential embodiment, the sensor device at the active site comprises at least two sensor elements for detecting radial position deviations of the rotor shaft, and the sensor elements and the operating elements at the active site are arranged in a plane extending vertically in relation to the plane of rotation. Preferably the operating elements are arranged in an angularly offset manner in respect to the sensor elements of the active site. Two operating elements are advantageously arranged offset by ninety degrees (90xc2x0) in the direction of rotation in respect to each other, and two sensor elements are also advantageously arranged offset by ninety degrees (90xc2x0) in the direction of rotation in respect to each other. A structurally compact embodiment of the damping device is thereby possible without a large outlay. The detection of radial positional deviations, as well as the control of the operating elements, can be performed simply and exactly. The control device is designed such that it is possible to take the angular offset of the operating and sensor elements into account during signal evaluation in a simple manner.
The damping force can be doubled in a simple manner if an additional operating element is assigned to each operating element and is located diametrically opposite in relation to the axis of rotation, and if the operating element and the additional operating element each act with the same force on the rotating magnetic element. Here, the force exerted by the operating element and the additional operating element is equal in its size as well as in its direction. The static magnetic forces acting on the rotating magnetic element, and therefore on the rotor shaft, which occur when operating elements are employed, each of which has a magnetic coil with an iron core for generating effective magnetic forces, can be neutralized with this embodiment.
The rotating magnetic element is preferably designed as a permanent magnet ring enclosing the rotor shaft, and the operating elements are preferably arranged at an axial distance in front of the permanent magnet ring. In this manner, it is possible to bring the operating elements very close to the rotating magnetic element, and the air gap between the magnetic element and the operating element can be kept small without interference by the bands around the exterior circumference of the magnetic element. Such bands are customarily placed around the magnetic rings of spinning rotors rotating at a high number of revolutions. The narrower the air gap between the operating element and the magnetic element, the greater the effectiveness of the damping which can be achieved.
The control device preferably has elements which are used for the exclusive capacitive decoupling of the signals generated by the sensor elements. Only the dynamic signal components are transmitted with such an embodiment. As a result, zero point errors of the sensor elements have no effect Because of the limitation of the a.c. portions, only small currents flow which, however, are sufficient for controlling the damping.
In comparison with known devices it is possible by means of the device in accordance with the invention to clearly improve the damping of radial oscillations. The desired optimum of damping can always be achieved without problems and without extensive optimization processes, because the damping effect is reproducible. By means of the invention it is possible without a great outlay to achieve damping which starts without delay and effectively.
Further details, features and advantages of the present invention will be described in the following specification of a preferred embodiment with reference to the accompanying drawings.